5
7
2
9
8
5
7
2
9
3
5
9
7
4
6
9
2
6
8
7
6
9
8
4
2
9
5
1
4
3
4
6
2
5
The brain releases dopamine when it solves a puzzle — the same reward chemical triggered by food and exercise.
The brain releases dopamine when it solves a puzzle — the same reward chemical triggered by food and exercise.
The number of essentially different Sudoku grids, accounting for symmetry, is 5,472,730,538 — about 5.5 billion.
The number of essentially different Sudoku grids, accounting for symmetry, is 5,472,730,538 — about 5.5 billion.